Particle therapy systems use an accelerator to generate a particle beam for treating afflictions, such as tumors. In operation, particles are accelerated in orbits inside a cavity in the presence of a magnetic field, and are removed from the cavity through an extraction channel. A magnetic field regenerator generates a magnetic field bump near the outside of the cavity to distort the pitch and angle of some orbits so that they precess towards, and eventually into, the extraction channel. A beam, comprised of the particles, exits the extraction channel.
A scanning system is down-beam of the extraction channel. In this context, “down-beam” means closer to an irradiation target (here, relative to the extraction channel). The scanning system moves the particle beam across at least part of the irradiation target to expose various parts of the irradiation target to the particle beam. For example, to treat a tumor, the particle beam may be “scanned” over different cross-sectional layers of the tumor.
The particle beam can damage healthy tissue adjacent to the irradiation target. A structure defining an edge may be used to limit exposure of the healthy tissue to the particle beam. For example, the structure, or a portion thereof, may be placed in between the particle beam and the healthy tissue, thereby preventing exposure of the healthy tissue to the particle beam.